The International Telecommunication Union Telecommunication Standardization Section (ITU-T) Recommendation H.323 and related H.323-series Recommendations, including the following are herein referred to individually and collectively as the H.323 Standard: ITU-T Recommendation H.323 (2000), Packet-Based Multimedia Communications Systems; ITU-T Recommendation H.225.0 (2000), Call Signaling Protocols and Media Stream Packetization for Packet Based Multimedia Communications Systems; ITU-T Recommendation H.225.0—Annex G (1999), Communication Between Administrative Domains; ITU-T Recommendation H.245 (2000), Control Protocol for Multimedia Communication; ITU-T Recommendation H.246 (1998), Interworking of H-Series Multimedia Terminals with H-Series Multimedia Terminals and Voice/Voiceband Terminals on GSTN and ISDN; ITU-T Recommendation H.246—Annex C (2000), ISDN User Part Function-H.225.0; ITU-T Recommendation H.235 (2000), Security and Encryption for H Series (H.323 and other H.245 based) Multimedia Terminals; ITU-T Recommendation H.450.1 (1998), Generic Functional Protocol for the Support of Supplementary Services in H.323; ITU-T Recommendation H.450.2 (1998), Call Transfer Supplementary Service for H.323; ITU-T Recommendation H.450.3 (1998), Call Diversion Supplementary Service for H.323; ITU-T Recommendation H.450.4 (1999), Call Hold Supplementary Service for H.323; ITU-T Recommendation H.450.5 (1999), Call Park and Call Pickup Supplementary Services for H.323; ITU-T Recommendation H.450.6 (1999), Call Waiting Supplementary Service for H.323; ITU-T Recommendation H.450.7 (1999), Message Waiting Indication Supplementary Service for H.323; ITU-T Recommendation H.450.8 (2000), Name Identification Supplementary Service For H.323; ISO/IEC 11571 (1998), Information Technology—Telecommunications and Information Exchange between Systems—Private Integrated Services Networks—Addressing; ITU-T Recommendation Q.931 (1998), ISDN User-Network Interface Layer 3 Specification for Basic Call Control; ITU-T Recommendation H.283, Remote Device Control Logical Channel Transport. 
H.323 is a standard that specifies components, protocols and procedures for implementing multimedia communication over packet-based networks. Examples of its application includes IP based telephony, video telephony, audio video and data, multipoint-multimedia communications, etc. H.323 networks comprise terminals, gateways, gatekeepers, and multipoint control units (MCU).
A gatekeeper is an H.323 entity on the network that provides services such as address translation and network access control for H.323 terminals, gateways and MCUs. Gatekeepers also provide services such as bandwidth management, accounting and dial plans. Gatekeepers are logically separated from H.323 endpoints such as terminals and gateways. Gatekeepers are optional in an H.323 network, but if a gatekeeper is present, end-points must use the services provided by the gatekeepers.
The registration admission and status (RAS) defines the call control services, including address translation, admissions control, zone management and bandwidth management. The gatekeeper controls and monitors call signaling messages between end-points.
The three distinct layers of a H.323 gatekeeper include the H.323 stack layer, gatekeeper core layer and gatekeeper application layer. The H.323 stack layer consists of basic registration admission and status (RAS), H.225, Q.931, H.245, Q.931, abstract syntax notation one (ASN.1) and RTP/RTCP stack functionalities. The gatekeeper core layer provides the gatekeeper infrastructure, where the H.323 messages received by the stack are put to context and call-control activity is performed. The gatekeeper application layer provides the application level access to the gatekeeper module for participating in the call-control activities.
The H.323 stack layer is the basic building block which takes care of initialization and setting up calls and channels, managing the calls and channels, and closing them. H.323 stack module receives all the messages from the transport packet (TPKT) layer and decodes the ASN.1 formatted message into a protocol value tree/protocol syntax tree (PVT/PST) structure for application access and manipulation.
The H.323 standard permits one and only one gatekeeper per zone. Application-aware service delivery appliances, such as media aggregators, aggregate voice and video traffic to and from enterprise sites enhance the performance of H.323 systems. There is a need for the inclusion of H.323 stack layer functionality within these media aggregators. The inclusion of H.323 stack layer functionality within these media aggregators enables the media aggregators to efficiently direct, aggregate and guarantee the end-to-end service quality of real-time traffic from site to site. However, in the H.323 systems, the H.323 stack layer functionality cannot be included in other devices such as a media aggregation manager because the H.323 standard permits only one gatekeeper per zone. Hence, there is a need to transparently introduce the H.323 stack layer functionality in devices such as the media aggregation manager.